1. Field of the Invention
The invention relates to a polyaxial bone anchoring system including a receiving part and at least a first bone anchoring element and, in some embodiments, a second bone anchoring element that are selectively connectable to the receiving part. Each of the first bone anchoring element and the second bone anchoring element is pivotable in the receiving part and can be fixed at a desired angle. The receiving part couples the bone anchoring element to a stabilization element such as a spinal rod. The first bone anchoring element can be pivoted in the receiving part to an enlarged maximum pivot angle that is greater than a maximum pivot angle of the second bone anchoring element. An orientation of the enlarged pivot angle can be selected within a range of 360° around a central axis of the receiving part, and may be automatically achieved by pivoting the receiving part relative to the bone anchoring element. Such a polyaxial anchoring device is a modular device, wherein the receiving part and the bone anchoring element are connectable by introducing the bone anchoring element from the bottom into the receiving part.
2. Description of Related Art
A polyaxial bone anchoring device with an enlarged pivot angle is described in U.S. Pat. No. 6,736,820. This bone anchoring device includes a bone screw and a receiving part with a seat for the head of the bone screw. The screw member can be pivoted to at least one side by an enlarged angle, because the edge bounding the free end of the receiving part is of asymmetric construction. In a modified embodiment, an insert piece is provided, which has a spherical bottom as a seat for the head of the screw member.
US 2007/0118123 A1 describes a polyaxial bone anchor with increased angulation. The polyaxial bone anchor has a locking element shaped and configured to allow an anchoring member, e.g. a screw or a hook, to polyaxially rotate at large angles about a central axis of the bone anchor before compression locking the anchoring member within an anchor head.